Rotary cathode x-ray tube equipment

ABSTRACT

The rotary cathode X-ray tube equipment of the present invention is constructed so as to permit radiation of X-ray from all directions with respect to the whole circumference of a subject, and is used for x-ray CT. The equipment of the invention is constructed to prevent an X-ray radiation window 40 of a low strength from being influenced by atmospheric deformations of a vacuum vessel 1 or by machining and assembling errors, for example by using a joint portion disposed between the X-ray radiation window and an inner ring and having both a surface perpendicular to a rotational axis of a rotary member and a cylindrical surface parallel to the rotational axis, a face seal formed on the surface of the joint portion perpendicular to the rotational axis, and an axial seal formed on the cylindrical surface of the joint portion parallel to the rotational axis.

This application is a continuation, of application Ser. No. 08/079,913,filed Jun. 23, 1993.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rotary cathode X-ray tube equipmentfor X-ray CT which is constructed so as to permit radiation of X-rayfrom all directions with respect to the whole circumference of asubject.

2. Description of the Prior Art

FIG. 1 is a sectional view of a conventional rotary cathode X-ray tubeequipment which is disclosed, for example, in Japanese Patent Laid OpenNo. 115738/83. In the same figure, a vacuum vessel 1 is installed on thefloor through a support base 2. The vacuum vessel 1 is in the form of aring provided centrally with a subject insertion hole 4 for passing asubject 3 therethrough. Its interior is maintained in high vacuum bymeans of a vacuum pump 5. An anode target 6 and a cathode portion 7 aredisposed at a predetermined spacing within the vacuum vessel 1, thecathode portion 7 being connected to brushes 8 and 9. Between thebrushes 8, 9 and the cathode portion 7 is provided a shielding plate 75so that dust resulting from wear of the brushes 8 and 9 may not movetoward the cathode portion 7, to which is applied a high voltage levelof about -70 kV.

The anode target 6 is for generating X-ray under the impingement thereonof an electron beam emitted from the cathode portion 7. It is formed ina ring shape and is rotatable about a rotational axis a. Morespecifically, the anode target 6 is fixed to a target rotor 11 through asupport member 10. The target rotor 11 is supported in a non-contactstate by means of a magnet 12 which is for magnetic levitation, and isgiven a rotating torque by a drive means (not shown) so as to rotatearound the rotational axis a. In operation, a high voltage level ofabout +70 kV is applied from the exterior to the target rotor 11 througha brush 13.

A touch-down bearing 14 is disposed near the target rotor 11, forsupporting the target rotor 11 when the power source for the magneticlevitation magnet 12 has turned off or when it has become impossible tocontrol the magnet 12 properly. During normal rotation of the targetrotor 11, the touch-down bearing 14 does not contact the same rotor.

On the other hand, the cathode portion 7 is ring-shaped and serves as acharged particle generating mechanism. It is fixed to a cathode-portionrotor 15. The cathode-portion rotor 15 is supported in a non-contactstate by means of a magnet 16 which is for magnetic levitation and whichis located inside the rotor 15, and is given a rotating torque by adrive means (not shown) so as to rotate about the rotational axis a inthe direction opposite to the target rotor 11. Consequently, the cathodeportion 7 rotates in the direction opposite to the anode target 6.Further, an X-ray radiation window 17 is provided, and near the window17 are disposed a collimator 18 and a ring-like detector 19 which iscoaxial with the rotational axis a.

In the vicinity of the cathode-portion rotor 15 there is provided atouch-down bearing 20 which has the same function as that of thetouch-down bearing 14. Between the brush 13 and the anode target 6 thereis disposed a shielding plate 76 so that dust resulting from wear of thebrush 13 may not move toward the anode target 6. The numerals 21 and 22each denote a brush for placing a cathode-side rotor 23 and ananode-side rotor 24 at earth potential. Numerals 77 to 81 each denote anelectrical insulator for insulation of a high voltage. Between theanode-side rotor 24 and the anode target 6 there is provided aninsulating material 82, and between the cathode-side rotor 23 and thecathode portion 7 there is provided an insulating material 83.

The following description is now provided about the operation of theconventional rotary cathode X-ray tube equipment shown in FIG. 1. First,an electron beam emitted from the cathode portion 7 impinges on a focalpoint 25 of the anode target 6. X-ray 26 generated from the focal point25 passes through the X-ray radiation window 17, then passes through thesubject 3 and thereafter enters the ring-shaped detector 19. An outputof the detector 19 is transmitted to a computer (not shown) for imagereconstruction by means of a data collection circuit (not shown) and isconverted to a coaxial tomography of the subject 3 in accordance with apredetermined reconstruction program.

In the conventional rotary cathode X-ray tube equipment constructed asabove, since the magnetic levitation magnets 12 and 16 are disposedoutside the vacuum vessel 1, the gap between each of the magnets 12, 16and the object attracted thereby becomes large. Therefore, it isnecessary for the magnets 12 and 16 to be strong. That is, the size,weight and power consumption of the rotary cathode X-ray tube equipmentare increased.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide a rotary cathode X-ray tube equipment in which deformations of avacuum vessel caused by the atmospheric pressure as well as machiningand assembling errors do not exert any influence on a portion which isstructurally low in strength.

It is another object of the present invention to provide a rotarycathode X-ray tube equipment which is far superior in accuracy andperformance to the existing equipment and which can be realized at arelatively low cost.

It is a further object of the present invention to provide a rotarycathode X-ray tube equipment which permits the omission of components,simplification of its structure and reduction in size of components, andfurther permits the reduction of its size, weight and cost.

It is still another object of the present invention to provide a rotarycathode X-ray tube equipment which permits mitigating demands concerningthe machining accuracy for components and further permits easy andinexpensive manufacture of components.

It is still further object of the present invention to provide a rotarycathode X-ray tube equipment of high reliability capable of improvingthe entire efficiency in comparison with the existing equipment.

According to the first aspect of the present invention, for achievingthe above-mentioned objects, there is provided a rotary cathode X-raytube equipment having a joint portion disposed between an-X-rayradiation window and an inner ring and provided with both a surfaceperpendicular to a rotational axis of a rotary member and a cylindricalsurface parallel to the said rotational axis, further having a face sealprovided on the surface of the joint portion perpendicular to therotational axis and an axial seal provided on the cylindrical surfaceparallel to the rotational axis.

Hence, in the rotary cathode X-ray tube equipment according to the firstaspect of the invention, atmospheric deformations in the rotational axisdirection as well as machining and assembling errors in the samedirection are absorbed by the face seal, while machining and assemblingerrors in the direction perpendicular to the rotational axis areabsorbed by the axial seal.

According to the second aspect of the present invention there isprovided a rotary cathode X-ray tube equipment in which an anode targetis placed at a high potential, while a cathode portion is placed at apotential close to the earth potential.

Hence, in the rotary cathode X-ray tube equipment according to thesecond aspect of the invention, it is not necessary to provideinsulation between the cathode portion and a rotor.

According to the third aspect of the present invention there is provideda rotary cathode X-ray tube equipment having a shielding plate made ofan electrically conductive material and disposed between an anode targetas well as a cathode portion and a filament current supply means as wellas a power conducting portion.

Hence, in the rotary cathode X-ray tube equipment according to the thirdaspect of the invention, the cathode portion and the anode target aredisposed on one side of the rotary member, while the power generatingportion and the power conducting portion are disposed on the other sideof the rotary member.

According to the fourth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment having a power conductinganode fixed to a rotary member and connected to a cathode portion andalso having a power conducting cathode fixed to a vacuum vessel andconnected to one end of a high voltage power supply, and in which theperveance between the power conducting cathode and the power conductinganode is set 100 times or more as large as the perveance between thecathode portion and the anode target.

Hence, in the rotary cathode X-ray tube equipment according to thefourth aspect of the invention, a non-contact connection is made betweenthe high voltage power supply and the cathode portion, and the potentialof the rotating portion is suppressed to below several hundred volts.

According to the fifth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment having an electromagnetfixed to a vacuum vessel and functioning to generate a magnetic field,and also having a power generating coil connected to filament andadapted to rotate together with a rotary member and thereby pass acrossthe magnetic field generated by the electromagnet.

Hence, in the rotary cathode X-ray tube equipment according to the fifthaspect of the invention, the supply of an electric current to thefilament is performed in a non-contact state.

According to the sixth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment having a magnetic fielddetector fixed to a vacuum vessel for detecting a magnetic field createdin a power generating coil by an electric current flowing through thesame coil.

Hence, in the rotary cathode X-ray tube equipment according to the sixthaspect of the invention, the electric current flowing in the powergenerating coil is detected by detection of the magnetic field createdby the same coil which detection is made by the magnetic field detector.

According to the seventh aspect of the present invention there isprovided a rotary cathode X-ray tube equipment in which a common magnetis used for both an electromagnet and a magnet for magnetic levitation.

Hence, in the rotary cathode X-ray tube equipment according to theseventh aspect, a magnet is used in common for both the electromagnetand the magnetic levitation magnet.

According to the eighth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment, in which at least aportion of a magnet for magnetic levitation is disposed within a vacuumvessel.

Hence, in the rotary cathode X-ray tube equipment according to theeighth aspect of the invention, the gap between the magnetic levitationmagnet and an object to be attracted becomes smaller.

According to the ninth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment in which opposed faces ofa magnet for magnetic levitation and an object to be attracted areinclined with respect to a rotational axis of a rotary member, and theattractive force of the magnetic levitation magnet has both a componentacting in the rotational axis direction and a component in the radialdirection of the rotary member.

Hence, in the rotary cathode X-ray tube equipment according to the ninthaspect of the invention, the magnet for magnetic levitation generatesattractive forces in two directions--one along the rotational axis ofthe rotary member and the other perpendicular thereto.

According to the tenth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment in which an object to beattracted is connected to both a rotary member and a rotor, the rotorbeing integral with the rotary member.

Hence, in the rotary cathode X-ray tube equipment according to the tenthaspect of the invention, the object to be attracted and the rotor aremade integral in construction.

According to the eleventh aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment having a plurality ofmagnets for magnetic levitation.

Hence, in the rotary cathode X-ray tube equipment according to theeleventh aspect of the invention, the size of each magnet for magneticlevitation is made smaller by using plural such magnets.

According to the twelfth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment in which the mountingposition of each magnet for magnetic levitation is adjustable.

Hence, in the rotary cathode X-ray tube equipment according to thetwelfth aspect of the invention, the position of each magneticlevitation magnet is adjusted at the time of mounting thereof.

According to the thirteenth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment having a plurality ofmagnets for magnetic levitation which are attached to an inner platemounted to a vacuum vessel.

Hence, in she rotary cathode X-ray tube equipment according to thethirteenth aspect of the present invention, the position of eachmagnetic levitation magnet attached to the inner plate is finelyadjusted.

According to the fourteenth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment in which, out of magnetfor magnetic levitation, the size of one having an attractive forcecomponent positioned in a direction of pulling up a rotary memberagainst gravity is larger than the size of one having an attractiveforce component positioned in a direction of pulling down the rotarymember.

Hence, in the rotary cathode X-ray tube equipment according to thefourteenth aspect of the invention, the size of a magnet for magneticlevitation which is not required to generate a large attractive force ismade smaller.

According to the fifteenth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment in which, out of thetotal number of magnets for magnetic levitation, the number of magnetshaving an attractive force component positioned in a direction ofpulling up a rotary member against gravity is larger than the number ofmagnets having an attractive force component positioned in a directionof pulling down the rotary member.

Hence, in the rotary cathode X-ray tube equipment according to thefifteenth aspect of the invention, the magnets for magnetic levitationlocated in positions not required to generate a large attractive forceare omitted.

According to the sixteenth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment having an inclinationangle detecting mechanism for detecting an inclination angle of a vacuumvessel and also having a levitation magnet control section which makescontrol in accordance with an output signal of the inclination angledetecting mechanism to increase an attractive force of a magneticlevitation magnet located in a position where its attractive force forpulling up a rotary member against gravity must be increased anddecrease an attractive force of a magnetic levitation magnet located ina position where the attractive force must be decreased.

Hence in the rotary cathode X-ray tube equipment according to thesixteenth aspect of the invention, an inclination angle of the vacuumvessel is detected by the inclination angle detecting mechanism, andupon tilting of the vacuum vessel, the attractive force of apredetermined magnet for magnetic levitation is increased by thelevitation magnet control section.

According to the seventeenth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment in which a front end of ayoke portion is disposed within a vacuum vessel.

Hence, in the rotary cathode X-ray tube equipment according to theseventeenth aspect of the invention, gas is evolved outside the vacuumvessel.

According to the eighteenth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment in which a non-contactdisplacement meter for detecting the position of a rotary member is usedand it measures a displacement of an inclined surface of an object to beattracted.

Hence, in the rotary cathode X-ray tube equipment according to theeighteenth aspect of the invention, the non-contact displacement meterperforms both detection of a levitation state of the rotary member anddetection of a rotary member position in the rotational axis direction.

According to the nineteenth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment using a non-contactdisplacement meter attached to an inner plate which is mounted to avacuum vessel.

Hence, in the rotary cathode X-ray tube equipment according to thenineteenth aspect of the invention, the mounting position of thenon-contact displacement meter attached to the inner plate is finelyadjusted.

According to the twentieth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment having at least onetouch-down bearing whose central axis is separate from the rotationalaxis of a rotary member.

Hence, in the rotary cathode X-ray tube equipment according to thetwentieth aspect of the invention, the central axis of the touch-downbearing is made separate from the rotational axis of the rotary memberto reduce the size of the same bearing.

According to the twenty-first aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment in which the mountingposition of a touch-down bearing used is adjustable.

Hence, in the rotary cathode X-ray tube equipment according to thetwenty-first aspect of the invention, there is performed a fineadjustment for the mounting position of the touch-down bearing.

According to the twenty-second aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment having a touch-downbearing attached to an inner plate which is mounted to a vacuum vessel.

Hence, in the rotary cathode X-ray tube equipment according to thetwenty-second aspect of the invention, the mounting position of thetouch-down bearing attached to the inner plate is finely adjusted.

According to the twenty-third aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment in which, within amovable range of a tilting mechanism, a centroid position of a portiontilted by the tilting mechanism never assumes a position verticallybelow the rotational axis of the tilting mechanism, and it is notcoincident with the rotational axis of the tilting mechanism.

Hence, in the rotary cathode X-ray tube equipment according to thetwenty-third aspect of the invention, the gravity of the portion tiltedby the tilting mechanism gives a unidirectional torque of a certainvalue or larger to a drive mechanism for the tilting mechanism.

According to the twenty-fourth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment having a torque applyingdevice for applying torque which is always unidirectional to a rotativeshaft of a tilt mechanism.

Hence, in the rotary cathode X-ray tube equipment according to thetwenty-fourth aspect of the invention, the torque applying deviceapplies a torque which is unidirectional and has a certain value orlarger to the drive mechanism for the tilting mechanism.

According to the twenty-fifth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment having a rotational angledetecting means for detecting a rotational angle of a rotary member, anon-contact displacement meter for detecting a position of the rotarymember, a memory section for storing a deformation quantity including amachining error and a detection error of the non-contact displacementmeter, and a deformation correcting circuit for correcting a detectedsignal at every rotational angle of the rotary member.

Hence, in the rotary cathode X-ray tube equipment according to thetwenty-fifth aspect of the invention, a rotational angle of the rotarymember is detected by the rotational angle detecting means, and adeformation quantity at every rotational angle is stored by the memorysection, which deformation quantity is corrected by the deformationcorrecting circuit.

According to the twenty-sixth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment having a drive means, thedrive means comprising a stator disposed on the side opposite to asubject insertion hole with respect to a vacuum vessel and a rotordisposed within the vacuum vessel and fixed to a rotary member.

Hence, in the rotary cathode X-ray tube equipment according to thetwenty-sixth aspect of the invention, the thickness of the equipment isreduced by disposing the stator on the side opposite to the subjectinsertion hole with respect to the vacuum vessel.

According to the twenty-seventh aspect of the present invention, thereis provided a rotary cathode X-ray tube equipment in which a stator usedis constituted by at least one rectilnear or arcuate stator, and thisrectilinear or arcuate stator and a rotor constitute a linear inductionmotor.

Hence, in the rotary cathode X-ray tube equipment according to thetwenty-seventh aspect of the invention, the mounting space for thestator is kept to a minimum required by forming the stator as at leastone arcuate stator.

According to the twenty-eighth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment in which the yoke facingportion of an outer ring is thinner than the yoke non-facing portionthereof.

Hence, in the rotary cathode X-ray tube equipment according to thetwenty-eighth aspect of the invention, the yoke facing portion of theouter ring is made thin while maintaining a required strength in thethicker portion of the outer ring.

According to the twenty-ninth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment in which an object to beattracted and a rotor-back yoke present on the back of a rotor areintegral with each other.

Hence, in the rotary cathode X-ray tube equipment according to thetwenty-ninth aspect of the invention, a rotary member is reinforced bythe object to be attracted which is high in rigidity.

According to the thirtieth aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment in which an encoder fordetecting a rotational angle of a rotary member is constituted by alight emitting portion and a light sensing portion which are disposed onboth sides of the rotary member and a plurality of detection holes ofthe rotary member formed in positions through which the light from thelight emitting portion passes.

Hence, in the rotary cathode K-ray tube equipment according to thethirtieth aspect of the invention, an encoder of a large diameter isconstituted by the light emitting portion, photosensor and detectionholes.

According to the thirty-first aspect of the present invention, there isprovided a rotary cathode K-ray tube equipment in which a light emittingportion and a light sensing portion are attached to inner plates whichare mounted to a vacuum vessel.

Hence, in the rotary cathode X-ray tube equipment according to thethirty-first aspect of the invention, the position of the light emittingportion and that of the light sensing portion attached to the innerplates are finely adjusted.

According to the thirty-second aspect of the present invention, there isprovided a rotary cathode X-ray tube equipment having a multiplyingcircuit, the multiplying circuit comprising a phase comparator to whichis inputted an output signal of an encoder, a VF converter forconverting an output signal of the phase comparator into a pulse havinga frequency proportional to the voltage thereof, and a frequency dividercircuit which counts pulses provided from the VF converter and outputsone pulse to the phase comparator at every counting of a preset number,the phase comparator comparing the phase of the output signal from theencoder with that of the output signal from the frequency dividercircuit.

Hence, in the rotary cathode X-ray tube equipment according to thethirty-second aspect of the present invention, the output signal of thephase comparator is converted to a pulse having a frequency proportionalto the voltage thereof by means of the VF converter, then the frequencyof the pulse is divided by the frequency divider circuit, and acomparison is made between the phase of the output signal from theencoder and that of the output signal from the frequency dividingcircuit by means of the phase comparator.

The above and further objects and novel features of the invention willmore fully appear from the following detailed description when the sameis read in connection with the accompanying drawing. It is to beexpressly understood, however, that the drawings are for purpose ofillustration only and are not intended as a definition of the limits ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a conventional rotary cathode X-raytube equipment;

FIG. 2 is a sectional view schematically showing a rotary cathode X-raytube equipment according to embodiment 1 of the present invention;

FIG. 3 is a partially enlarged view of FIG. 2;

FIG. 4 is a detailed view of the rotary cathode X-ray tube equipmentshown in FIG. 2;

FIG. 5 is a construction diagram schematically showing in what manner anoutput signal from a detector is processed;

FIG. 6 is a flowchart showing operations of a deformation correctingcircuit;

FIG. 7 is a block diagram showing a construction of the deformationcorrecting circuit;

FIG. 8 is a block diagram showing the details of a multiplying circuit;

FIG. 9 is a construction diagram showing in what manner a magnet formagnetic levitation is mounted;

FIG. 10 is an explanatory view of embodiment 3 of the present invention;

FIG. 11 is a block diagram showing a construction of embodiment 3 of thepresent invention; and

FIG. 12 is a construction diagram schematically showing embodiment 4 ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail hereinunder referring to the accompanying drawings.

Embodiment 1

First, an outline of embodiment 1 will be given with reference to FIGS.2 and 3. FIG. 2 is a sectional view illustrating a rotary cathode X-raytube equipment according to embodiment 1 of the present invention, andFIG. 3 is a partially enlarged view of FIG. 2, in which figures theportions equal or corresponding to those shown in FIG. 1 are indicatedby the same reference numerals as in FIG. 1 and explanations thereofwill be omitted. In FIGS. 2 and 3, a vacuum vessel 1 is composed of anouter ring 1a, an inner ring 1b and two side plates 1c. Within thevacuum vessel 1 there is disposed a disk-like rotary member 28fabricated of aluminum or the like, and objects 29 to be attracted,which are made of a magnetic material, are fixed to the rotary member28. Further, in an opposed state to the objects 29 to be attracted,magnets 30 for magnetic levitation are attached to the side plates 1c ofthe vacuum vessel 1 each through an inner plate 61.

A magnetic levitation mechanism is constituted by the objects 29 to beattracted and the magnetic levitation magnets 30. The rotary member 28is supported rotatably about a rotational axis a thereof by means of themagnetic levitation mechanism. On the side opposite to a subjectinsertion hole 4 with respect to the vacuum vessel 1 there are disposedstators 31, which are fixed to the outer ring la of the vacuum vessel 1.Within the vacuum vessel 1, a rotor 32 formed of a aluminum or the likeis disposed in close proximity to the stators 31. A drive means isconstituted by the stators 31 and votors 32.

A cathode portion 7 is fixed to the rotary member 28 and it rotatesaround the rotational axis a together with the rotary member 28. Aring-like anode target 6 disposed in an opposed relation to the cathodeportion 7 is fixed to a side plate 1c of the vacuum vessel 1 with anelectric insulator 33. Within the cathode portion 7 is accommodated afilament 34 for the emission of thermoelectrons, and a power generatingportion 35 for supplying an electric current to the filament 34 isdisposed on the side opposite to the cathode portion 7 with respect tothe rotary member 28. The power generating portion 35 is composed of anelectromagnet 36 and a power generating coil 37. Near the powergenerating portion 35 is disposed a power conducting portion 38 forapplying a high voltage between the anode target 6 and the cathodeportion 7 which voltage is provided from a high voltage power supply 39.An X-ray radiation window 40 is attached to the inner ring 1b of thevacuum vessel 1. The rotary cathode X-ray tube equipment can tilt arounda subject 3 under the operation of a tilting mechanism 71 (see FIG. 10).

Now, the operation of embodiment 1 of the present invention illustratedin FIGS. 2 and 3 will be outlined. The rotary member 28 is supported bythe magnetic levitation mechanism and is rotated about the rotationalaxis a by the drive means. In this state, the filament 34 is heated byan electric current supplied from the power generating portion 35, andwhen a voltage provided from the high voltage power supply 39 is applieda between the anode target 6 and the cathode portion 7 (the anode target6 is placed at a high voltage and the cathode portion 7 substantially atthe earth potential), thermoelectrons are emitted from the cathodeportion 7 and impinge against a focal point 25 on the anode target 6.X-ray 26 is generated from the focal point 25 and is radiated from theX-ray radiation window 40 which is ring-like. Subsequent operations arethe same as in the prior art, so descriptions thereof are omitted here.

Features of embodiment 1 will now be described in detail. As shown inFIGS. 2 and 3, since the X-ray passing portion of the X-ray radiationwindow 40 is thin-walled, having a thickness of 4 to 5 mm, the vacuumvessel 1 is reinforced by reinforcing beams 84 so that the atmosphericpressure from the side plates 1c may not be exerted on the X-ray passingportion. Eight reinforcing beams 84 are provided on each side plate 1cof the ring-like vacuum vessel 1, so a total of sixteen beams 84 areprovided in total. However, with only the reinforcing beams 84, it isimpossible to completely prevent the influence of the atmosphericpressure. Further, since the subject insertion hole 4 is present in thevacuum vessel 1 and the same vessel is large-sized, having an outsidediameter of 1,400 mm and an inside diameter of 800 mm, it is difficultto enhance the machining accuracy for the outer and inner rings 1a, 1band two side plates 1c, as well as their assembling accuracy, sometimesresulting in that an extra force is exerted on the X-ray radiationwindow 40.

In view of the above points, a joint portion 90 having a surface 85perpendicular to the rotational axis of the rotary member 28 and acylindrical surface 86 parallel to the rotational axis is providedbetween the X-ray radiation window 40 and the inner ring 1b, and furtherthere also is provided a face seal 87. Consequently, atmosphericdeformations and machining and assembling errors in the rotational axisdirection can be absorbed by an axial seal 89, while machining andassembling errors in the direction perpendicular to the rotational axiscan be absorbed by face seals 87, 88, so that no extra force is appliedto the X-ray radiation window 40. It is necessary to fabricate the jointportion 90 and the inner ring 1b using materials whose thermal expansioncoefficients are closely akin to each other so that the size of the gapwherein the axial seal 89 is disposed may not greatly change againsttemperature changes.

In the case of applying a high voltage approximately 120 to 130 kV, thewhole of the vacuum vessel 1 is placed at the earth potential, thecathode portion 7 approximately at the earth potential (as will bedescribed later) and the anode target 6 at high voltage. In the case ofplacing the anode target 6 at the earth potential and the cathodeportion 7 at a negative high voltage level, or in the case of settingthe anode target 6 at +60 to +65 kV and the cathode portion 7 at -60 to-65 kV, making a neutral earthing, it is necessary to insulate betweenthe cathode portion 7 and the rotor 32. This is because otherwisedischarge would occur since the rotor 32 and the vacuum vessel 1 areclose to each other. In this construction, since the portion whereinsulation should be made against a high voltage is only the anodetarget 6, it is possible to stabilize performance and attain thereduction of cost.

An electric insulator 33 is attached to a side plate 1c of the vacuumvessel 1, then an annular cooling ring 94 is attached to the insulator33, and the anode target 6 is attached to the ring 94. The anode target6 is fixed at an incline so that the X-ray 26 faces toward the subject3. Since the electric insulator 33 is mounted to the side plate 1c in aposition where a reinforcing beam 84 for preventing an atmosphericdeformation of the side plate is present, the position of the anodetarget 6 is not influenced by the atmospheric pressure, thus permittinggeneration of a highly accurate rotary X-ray. The interior of thecooling ring 94 is filled with a cooling medium which is superior inelectrical insulation property. The cooling medium absorbs the heat ofthe anode target 6, then passes through a coolant pipe (not shown) andis heat-exchanged by means of a radiator (not shown) which is mountedoutside the vacuum vessel 1, thereafter returns to the cooling ring 94.The coolant pipe is also formed by a material superior in electricalinsulation property.

Filament 34 for generating thermoelectrons is disposed in the interiorof the cathode portion 7, constituting an electronic lens for convergingthe generated electrons onto the focal point 25 of the anode target 6.Since the filament 34 has a life span such that it will become finer dueto vacuum evaporation and finally break, a consideration is given topermit easy replacement of the cathode portion 7. More specifically, aflange (not shown) is provided in a position of a side plate 1ccorresponding to the cathode portion 7 to permit replacement of thecathode portion 7 without removal of the entire side plate 1c. Further,to maintain a rotational balance, plural cathode portions of the sameshape are disposed so that in the event of disconnection of onefilament, connection can be changed to supply an electric current toanother filament.

As shown in FIG. 3, the rotary member 28 divides the interior of thevacuum vessel 1 into two portions, in one of which are disposed theX-ray generating cathode portion 7 and anode target 6, while in theother there are disposed the power generating portion 35 and powerconducting portion 38 involving the evolution of gas. Therefore, it ispossible to maintain the cathode portion 7 and anode target 6 in a stateof high vacuum. This is made more effective by the arrangement on theside of the cathode portion 7 of a vacuum pump 5 and the anode target 6.The vacuum pump 5 is disposed in a position which does not interferewith the subject 3 at the time of tilting. An additional vacuum pump maybe disposed on the side of the power generating portion 35, etc. Sincethe rotary member 28 is fabricated of an electrically conductivematerial such as aluminum, it is possible to prevent the occurrence ofdischarge between the anode target 6 which is brought into the state ofhigh voltage and the power generating portion 35, etc., whereby a stableX-ray can be obtained.

As shown in FIG. 2, the power conducting portion 38 comprises powerconducting cathodes 91 each constituted by a tungsten strand of 0.22 mmdie. by 28 mm long and disposed in several positions throughout thewhole circumference in the vacuum vessel 1, and a power conducting anode92 of 3.5 mm in radius which is disposed in a surrounding relation tothe power conducting cathodes 91 throughout the whole circumference ofthe vessel 1. The power conducting cathodes 91 have a power conductingfilament (not shown) which is heated by an external power supply 93,whereby thermoelectrons are emitted from the power conducting cathode91. The power conducting anode 92 is as large as 1 m or so in diameterand since a thermal expansion with the rise of temperature caused byelectron impingement and radiation from the power conducting filament isnot negligible, the anode 92 is constituted in a divided manner, not asan integral body. Further, the power conducting anode 92 has a blackcoating on the surface thereof to permit easy escape of heatradiationwise to the vacuum vessel 1 side. As the power conductingfilament there usually is employed a thermoelectron emitting materialsuch as, for example, tungsten or thoriated tungsten, but no speciallimitation is placed thereon if only the material used is an electronemitting source.

Since the power conducting anode 92 levitates in vacuum, the perveancebetween the power conducting cathodes 91 and the power conducting anode92 is set 100 times or more as high as the perveance between the cathodeportion 7 and the anode target 6, and operation is performed in a spacecharge limited range, it is possible to suppress the potential of theanode 92, namely, the potential of the rotating portion, to a value ofbelow several hundred volts. Consequently, not only it is possible tosuppress a vacuum discharge between adjacent vacuum vessel 1 and therotor 32, but also it is possible to diminish the variation in apotential difference applied between each cathode portion 7 and anodetarget 6, whereby a good image quality can be obtained. Further, thegeneration of heat of the power conducting anode 92 caused by electronicshock can be prevented. In this embodiment wherein the power conductingcathodes 91 and anode 92 are constructed and arranged in the foregoingmanner, a potential difference between the two was 180 V and aconduction current was 200 mA.

Several tens of power generating coils 37 are fixed to the rotary member28 at equal pitches throughout the whole circumference and are connectedto the filaments 34. Several electromagnets 36 are fixed each through aflange 95 to a side plate 1c of the vacuum vessel 1 in positionscorresponding to the power generating coils 37. The power generatingportion 35 is constituted by each electromagnet 36 and power generatingcoil 37. The coils 37 are each disposed in such a manner as to passbetween pole pieces of the associated electromagnet 36, and withrotation of the rotary member 28, the coils 37 traverse the magneticfields of the electromagnets 36 to generate electric power. A yokeportion of each electromagnet 36 is vacuum-sealed and extends throughthe flange 95, and a coil portion thereof is placed in the air. Thus,consideration is given so that the release of gas due to the generationof heat during energization of the coil is performed in the air.

Thus, the magnetic fields to be imparted to the power generating coils37 are created by only the electromagnets 36 without the aid ofpermanent magnets. In a power generation system using permanent magnetsin combination with electromagnets, the generation of heat caused by aneddy current can be controlled by only the number of revolutions of therotary member 28, so that the rise of temperature in vacuum causes theevolution of gas and hence the resulting X-ray is not stable. This isundesirable. On the other hand, in the power generation system usingonly the electromagnets 36, by making electric currents in theelectromagnets 36 opposite to each other in the direction of flow, it ismade possible to allow filaments not to turn on, allowing only the powergenerating coils 37 to exhibit a rise in temperature due to an eddycurrent, thereby permitting promotion of vacuum exhaust.

In order to keep the intensity of the resulting X-ray 26 constant, it isnecessary to detect an electric current flowing between the cathodeportion 7 and the anode target 6 and make it constant. In this end, itis effective to adjust the voltage generated in each power generatingcoil 37 and thereby to control the electric current in the filament 34.Adjustment of the voltage generated in the coil 37 can be made bydetecting an AC magnetic field induced by the electric current in thecoil 37 and then making it constant, using Hall element (a magneticfield detecting element, not shown) provided on the plane through whichthe coil 37 passes. Particularly, since the coil 37 is placed in vacuum,it is not cooled with air, and hence the coil 37 exhibits a largeincrease of its temperature due to the generation of heat induced byelectric resistance or eddy current. Such a rise of temperatureincreases the electric resistance of the filament 34, diminishes theelectric current in the filament and decreases the intensity of theX-ray 26, the Hall element is very effective in obtaining a stable X-ray26.

Since all that is required for the electromagnets 36 is that theelectromagnets should be disposed within and fixed to the vacuum vessel1, it is also possible to let the magnets 30 for magnetic levitationfunction as the electromagnets 36.

As shown in FIG. 3, the magnetic levitation magnets 30 are disposedwithin the vacuum vessel 1. Therefore, the magnets 30 and the objects 29to be attracted can be opposed to each other directly not through thewall of the vessel 1, so that the gap between the two becomes smaller.Consequently, it is no longer necessary for the magnets 30 to be strong,and their size and weight and power consumption are reduced. Foravoiding atmospheric deformations of the vacuum vessel 1, the magnets 30are attached to the inner plates 61 which are separated mechanicallyfrom the vessel 1. Further, one end of each of the inner plates 61extend toward the rotary member 28 to provide a vacuum separationstructure so that the gas generated from the magnets 30 may not movetoward the anode target 6 and the cathode portions 7. The inner plates61 are formed of a material having a high magnetic permeability so thatthermoelectrons from the cathode portions 7 may not be deflected by themagnetic field leaking from the magnets 30.

The opposed faces of each object 29 to be attracted and magneticlevitation magnet 30 are both inclined 45° relative to the rotationalaxis a. Therefore, with only one magnet 30, it is possible to move therotary member 28 in both the direction of the axis a and the directionperpendicular thereto, that is, it is no longer required to use magneticlevitation magnets respectively for movement in the rotational axis adirection and movement in the direction perpendicular thereto.

As shown in FIG. 3, the objects 29 to be attracted are fixed to theconnection between the rotary member 28 and the rotor 32. The rotarymember 28 and the rotor 32 are formed of a material low in rigidity suchas aluminum for example and so the objects 29 to be attracted play therole of reinforcing the rotary member 28 and the rotor 32. Further, arotor-back yoke 32a present at the back of the rotor 32 is integral witheach object 29 to be attracted.

As shown in FIG. 4(b), it is not that a single magnet 30 for magneticlevitation is provided throughout the whole circumference, but there areused a total of twelve such magnets 30 in a divided manner. As a result,each magnet 30 becomes smaller in size and so is easier to handle.

The mounting positions of the magnetic levitation magnets 30 can befinely adjusted. More specifically, in mounting the magnets 30, all themagnets 30 are first attached to the inner plates 61 with bolts 62, asshown in FIG. 9(a). In this case, there are used mounting holes 63,which are vertically long as shown in FIG. 9(b) and which permit fineadjustment of the mounting position of each magnet 30, therebypermitting fine adjustment of the gap between the magnet 30 and theassociated object 29 to be attracted. The inner plates have beensubjected to spot facing to receive the heads of the bolts 62 therein.After the end of mounting of all the magnets 30 for magnetic levitation,the inner plates 61 are fixed to the side plates 1c of the vacuum vessel1.

As shown in FIG. 4(b), the number of the magnets 30 is larger (eight inall) in the lower portion and smaller (four in all) in the upperportion. This is because the attraction component of the magnets 30disposed in lower positions face in a direction to pull up the rotarymember 28 against gravity, while the attraction component of the magnets30 disposed in upper positions face in a direction (same as thegravitational direction) to pull down the rotary member 28.Particularly, for magnetic levitation of such a heavy object as therotary member 28, such difference in the number of magnets 30 is veryeffective.

Although in FIG. 3 both yoke and coil portions 30a, 30b of the magneticlevitation magnets 30 are disposed within the vacuum vessel 1, there maybe adopted a construction in which only the yoke portions 30a aredisposed within the vacuum vessel 1 and the coil portions 30b disposedoutside the vessel 1. Since the coil portions 30b evolve gas, it ispossible to improve the degree of vacuum of the vacuum vessel 1.

FIGS. 4(a) and 4(b) are detailed views of the rotary cathode X-ray tubeequipment shown in FIG. 2, in which FIG. 4(a) is a front view and FIG.4(b) is a side view. There are constructional elements which are notshown in FIGS. 4(a) and 4(b) though shown in FIGS. 2 and 3. In FIG. 4, atotal of eight non-contact displacement meters 41 are disposed in closeproximity to slant faces 29a of the objects 29 to be attracted. Thenon-contact displacement meters 41 are for detecting positions of theobjects 29 and thereby detecting the state of magnetic levitation of therotary member 28. Detected signals from the meters 41 are processed by amagnet control circuit 53 (see FIG. 5) to control the magnets 30. Thus,the non-contact displacement meters 41 measure displacements of theslant faces 29a and hence the position of the rotary member 28 in therotational axis a direction and the position thereof in the directionperpendicular thereto can be detected by one displacement meter 41; thatis, it is not necessary to provide non-contact displacement metersrespectively for the measurement in the rotational axis a direction andfor the measurement in the direction perpendicular thereto. The sideplates 1c of the vacuum vessel 1 are formed with lead wire passingportions 42 (see FIG. 5).

The non-contact displacement meters 41 can be mounted to the innerplates 61, whereby it is made possible to facilitate fine adjustment ofthe mounting positions of the meters 41.

As shown in FIG. 4(b), touch-down bearings 60 are disposed so as to havea different central axis than the rotational axis a of the rotary memberand thus they are different from the conventional touch-down bearings(see those indicated at 14 and 20 in FIG. 1). Since the rotary cathodeX-ray tube equipment has a large subject insertion hole 4 formedcentrally, the conventional arrangement requires using touch-downbearings of a large diameter. Although it is necessary to use a largenumber (16 in this embodiment) of touch-down bearings 60, as shown inFIG. 4, there can be attained reduction in size, weight and cost ascompared with using one or two bearings of a large diameter. Thefunction of the touch-down bearings 60 is the same as in the prior art;that is, they function to support the rotary member 28 when the powersource of the magnetic levitation mechanism has been turned off.

The touch-down bearings 60 can be mounted to the inner plates 61,whereby it is made possible to facilitate fine adjustment of themounting positions of the bearings 60.

FIG. 6 is a flowchart showing operations of a deformation correctingcircuit for correcting deformations of the rotary member 28 caused bymachining errors, gravitational deformations, etc. Prior to performingthe operations shown in this flowchart, a jig (not shown) having acentroid indicating point which indicates a centroid position of therotary member 28 is mounted centrally of the rotary member. This jig ismounted after removal of the inner ring 1b of the vacuum vessel 1.Further mounted is an auxiliary sensor (not shown) for detecting theposition of the centroid indicating point.

Reference will now be made to operations of steps S₁ to S₄ which areperformed prior to operation (coaxial tomography obtaining operation) ofthe rotary cathode X-ray tube equipment for obtaining a coaxialtomography of the subject. First, an output signal A1 from thenon-contact displacement meters 41 and an output signal A₂ from theabove auxiliary sensor are taken in (step S₁). The output signal A₁contains a deformation quantity of the rotary member 28, while theoutput signal A₂ does not contain such deformation quantity. Therefore,the deformation quantity can be calculated by subtraction between bothoutput signals (step S₂). This deformation quantity is stored in thememory portion of RAM for example (step S₃). Then, the operations ofsteps S₁ to S₃ are performed while the rotary member 28 is turnedstepwise, say, 1° at a time, and a deformation quantity in one rotationis stored (step S₄). Thereafter, the jig and the auxiliary sensor areremoved.

Next, the operation flow shifts to a coaxial tomography obtainingoperation comprising steps S₅ to S₉. This operation is carried out bythe deformation correcting circuit 53 shown in FIG. 7. First, arotational angle signal 28a indicating a rotational angle of the rotarymember 28 is taken in from a rotational angle detecting means, or anencoder which will be described later, (step S₅). Since there is thepossibility that the encoder will make a mistake in counting, thiscounting error is corrected by an initial angle signal which isgenerated one per rotation of the rotary member 28 (steps S₅ and S₆). Inthis way there is obtained an accurate rotational angle of the rotarymember 28, so a deformation quantity corresponding to the rotationalangle is accessed from a memory section 48 (step S₇). This deformationquantity is converted to a control signal correcting quantity for themagnetic levitation magnets 30 by means of an arithmetic section 47(step S₈). The said control signal correcting quantity is added to anoutput signal of a centroid position computing section 44, which signalis then outputted to a levitation magnet control section 70 (step S₉).Further, an output signal from the control section 70 is amplified by anamplifier 45 and then fed to the magnetic levitation magnets 30.

As shown in FIGS. 2 and 4, the stators 31 are disposed outside the outerring la of the vacuum vessel 1, that is, on the side opposite to thesubject insertion hole 4 with respect to the vessel 1. This arrangementis advantageous in the following points in comparison with theconventional arrangement in which the stators are disposed on the sideplates 1c of the vessel 1. The thickness (distance b in FIG. 2) of therotary cathode X-ray tube equipment can be made small and hence it ispossible to enlarge the movable range (an angular range which permitsrotation of the rotary cathode X-ray tube equipment around the subject3) of the tilting mechanism 71 (see FIG. 10). On the other hand, even incomparison with the case where the stators are disposed on the innerring 1b of the vacuum vessel 1, the subject insertion hole 4 is largerand therefore it is possible to inspect even a large subject 3; besides,the movable range of the tilting mechanism 71 becomes wider. It is alsopossible to enlarge the whole machine while maintaining the subjectinsertion hole 4 and dispose the stators inside the inner ring 1b, butsince the X-ray generating position assumes an outside position, thereoccur drawbacks such as, for example, a poor utilization efficiency ofX-ray.

The shape of the stators 31 is not circular, unlike the conventionalshape, but is arcuate as in FIG. 4(b). Together with the rotor 32 in thevacuum vessel 1, the stators 31 constitute a linear induction motor. Inconsideration of controlling the levitation of the rotary member 28 andin order to prevent its rotational center from becoming eccentric, it isnecessary that the stators 31 be disposed in two or more positions (twoin the vertical direction) at equal intervals.

As shown in FIG. 3, the thickness of the outer ring 1a is smaller in theportion where the yoke part of each stator 31 is positioned than in theportion where such yoke part is not present. As a result, the drivingforce of the motor can be increased at the thinner portion whileretaining a required strength at the thicker portion.

As shown in FIG. 4(b), a plurality of detection holes 50 are formed inthe rotary member 28, and as shown in FIG. 4(a), a light emitter 51 anda photosensor 52 are disposed on both sides of the detection holes 50.When a detection hole 50 arrives at the spacing between the lightemitter 51 and the photosensor 52 in accordance with the rotationalangle of the rotary member 28, the light from the light emitter 51reaches the photosensor 52, while when no detection hole 50 is presentin the spacing, the light from the light emitter 51 does not reach thephotosensor 52. By processing an output signal provided from thephotosensor 52, it is made possible to detect a rotational angle of therotary member 28 from its initial position or a rotating speed thereof.Thus, the detection holes 50, light emitter 51 and photosensor 52constitute a large encoder centered on the rotational axis a of therotary member 28. The detection accuracy thereof is very high because ofa large distance from the axis a to each detection hole 50, and thereliability is also high because it is a non-contact type.

As shown in FIG. 5, an output signal from the above encoder is amplifiedby a photosensor amplifier 54 and is then eight-multiplied by amultiplying circuit 55. FIG. 8 is a block diagram showing the details ofthe multiplying circuit 55. The output signal from the encoder is firstfed to a phase comparator 56, which in turn outputs a voltageproportional to a phase difference between two input signals. An outputsignal from the phase comparator 56 is filtered by means of a filter 57and thereafter converted to a pulse having a frequency proportion to thevoltage by means of a VF converter 58.

Since the gain of the phase comparator 56, etc. is adjusted properly,the pulse has an eight-multiplied frequency with respect to the encoderoutput signal. This eight-multiplied signal is fed to a frequencydivider circuit 59, which in turn outputs one pulse at every counting ofeight pulses. Consequently, the output pulse from the frequency dividercircuit 59 comes to have a frequency equal to that of the encoder outputsignal. This output pulse is fed back to the phase comparator 56, whichin turn outputs a voltage proportional to a phase difference between theencoder output signal and the output signal from the frequency dividercircuit 59, thereby resulting in that the ratio between the frequency ofthe encoder output signal and that of the eight-multiplied signalbecomes just 8.

Embodiment 2

Although in embodiment 1 the attracting force in the direction to pullup the rotary member 28 is increased by differentiating the number ofthe magnetic levitation magnets 30, the same effect can be attained alsoby increasing the size of the magnets 30 disposed in the lower portion.

Embodiment 3

An X-ray CT equipment is usually provided with the tilting mechanism 71for tilting an X-ray generating mechanism (the vacuum vessel 1 in therotary cathode X-ray tube equipment of the present invention) withrespect to the subject 3, as shown in FIG. 10. When the vacuum vessel 1tilts, the rotary member 28 accommodated in the vessel also tilts, sothe attractive force to be generated by each magnetic levitation magnetmust vary.

More specifically, when an inclination angle θ is 0, the attractiveforce to be generated by a magnet 30a for magnetic levitation and thatby a magnet 30b for magnetic levitation are the same, and the attractiveforces to be generated by magnetic levitation magnets 30c and 30d arethe same. However, when the inclination angle θ increases into such astate as shown in FIG. 10, the attractive force to be generated by themagnet 30a is required to be larger than that to be generated by themagnet 30b; likewise, the attractive force to be generated by the magnet30c must be larger than that to be generated by the magnet 30d. Suchvariations in attraction causes variations in the electric currentsupplied to each magnet 30 for magnetic levitation, thus sometimescausing the control for the magnetic levitation mechanism to becomeunstable.

Such unstabilization problem is solved by increasing the attractiveforce of the magnetic levitation magnet 30a which is disposed so thatits attractive force component is enhanced for pulling up the rotarymember 28 against gravity. More specifically, an inclination anglesensor 72, e.g. encoder, for detecting an inclination angle θ isdisposed near the tilting mechanism 71 so that an inclination anglesignal 73 indicating the inclination angle θ is inputted to thelevitation magnet control section 70, as shown in FIG. 11. The controlsection 70 outputs to the amplifier 45 an electric current controlsignal with a bias proportional to the inclination angle θ addedthereto. In this way it becomes possible to stably control theattractive force of each magnet 30 for magnetic levitation.

As shown in FIG. 10, the rotational axis of the tilting mechanism 71 isdisposed in a deviated state so that the centroid position of theportion (vacuum vessel 1, etc.) which is tilted by the tilting mechanism71 is neither vertically below the rotational axis of the tiltingmechanism nor on the rotational axis. Consequently, the gravity whichworks on the vacuum vessel 1, etc. imparts a unidirectional torque of acertain value or more to the drive source of the tilting mechanism 71.By so doing, it is made possible to prevent the vacuum vessel 1, etc.from being oscillated about the rotational axis by a reaction to theattractive force of the magnetic levitation magnets 30.

Embodiment 4

As shown in FIG. 12, the same effect as that mentioned in the latterhalf portion of embodiment 3 can be obtained also by attaching a weight96 to the portion which is tilted by the tilting mechanism 71 to let aunidirectional torque of a certain value or more act on a tilting motor97 through a chain 98.

According to the rotary cathode X-ray tube equipment in the first aspectof the present invention, since the equipment is provided with a jointportion disposed between an X-ray radiation window and an inner ring andhaving both a surface perpendicular to a rotational axis of a rotarymember and a cylindrical surface parallel to the rotational axis theequipment is, further provided with a face seal formed on the surfaceperpendicular to the rotational axis of the joint portion and an axialseal formed on the cylindrical surface parallel to the rotational axis.Therefore, the X-ray radiation window which is low in strength is notinfluenced by atmospheric deformations of the vacuum vessel or machiningand assembling errors.

According to the rotary cathode X-ray tube equipment in the secondaspect of the present invention, since the anode target is set at a highpotential, with the cathode portion at a potential close to the earthpotential, it is possible to prevent discharge between the rotor and thevacuum vessel. Additionally since it is only the anode target 6 thatshould be insulated with respect to a high voltage, it is possible tostabilize performance and attain the reduction of cost.

According to the rotary cathode X-ray tube equipment in the third aspectof the present invention, since the equipment is provided with ashielding plate made of an electroconductive material and disposedbetween the anode target as well as the cathode portion and the filamentcurrent supply means as well as the power conducting portion, it ispossible to prevent gas generated in the filament current supply meansand the power conducting portion from moving toward the anode target andthe cathode portion and thereby keep the anode target and the cathodeportion in high vacuum. It is also possible to prevent the occurrence ofdischarge between the filament current supply means as well as the powerconducting portion and the anode target as well as the cathode portion.

According to the rotary cathode X-ray tube equipment in the fourthaspect of the present invention, the equipment is provided with a powerconducting anode fixed to the rotary member and connected to the cathodeportion and also provided with a power conducting cathode fixed to thevacuum vessel and connected to one end of a high voltage power supply,and the perveance between the power conducting cathode and the powerconducting anode is set 100 times or more as large as the perveancebetween the cathode portion and the anode target. Since the high voltagepower supply and the cathode portion can be connected in a non-contactmanner, there no longer is any fear of wear or dust, resulting in aprolonged service life of those components. Further, since it ispossible to diminish variations in the potential difference between thecathode portion and the anode target, a good image quality can beobtained.

According to the rotary cathode X-ray tube equipment in the fifth aspectof the present invention, since the equipment is provided with anelectromagnet fixed to the vacuum vessel and functioning to generate amagnetic field and also provided with a power generating coil connectedto filament and adapted to rotate together with a rotary member andthereby pass across the magnetic field generated by the electromagnet,the supply of electric power to the filament can be done in anon-contact state and hence there is no longer any fear of wear or dust,resulting in a prolonged service life.

According to the rotary cathode X-ray tube equipment in the sixth aspectof the present invention, since the equipment is provided with amagnetic field detector fixed to the vacuum vessel for detecting amagnetic field created in a power generating coil by an electric currentflowing through the same coil, the electric current fed to filament ismade constant and it is thereby made possible to obtain a stable X-ray.

According to the rotary cathode X-ray tube equipment in the seventhaspect of the present invention, since a common magnet is used for bothan electromagnet and a magnet for magnetic levitation, it is possible toreduce the number of parts used and hence attain the reduction of weightand cost.

According to the rotary cathode X-ray tube equipment in the eighthaspect of the present invention, since at least a portion of a magnetfor magnetic levitation is disposed within the vacuum vessel, themagnetic levitation magnet and an object to be attracted can be opposedto each other without through the wall of the vacuum vessel and the gapbetween the two can be made smaller, so it is possible to reduce thesize, weight and power consumption of the magnetic levitation magnet.

According to the rotary cathode X-ray tube equipment in the ninth aspectof the present invention, opposed faces of the magnetic levitationmagnet and the object to be attracted are both inclined with respect tothe rotational axis of the rotary member, and the attractive force ofthe magnetic levitation magnet involves both a component acting in therotational axis direction and a component in the radial direction of therotary member, so the magnetic levitation magnet can generate at a timeboth a force acting in the rotational axis direction of the rotarymember and a force in the direction perpendicular thereto, whereby it ismade possible to reduce the size, particularly the size in therotational axis direction.

According to the rotary cathode X-ray tube equipment in the tenth aspectof the present invention, since the object to be attracted and the rotorare integral with each other, it is possible to attain the reduction ofweight and cost.

According to the rotary cathode X-ray tube equipment in the eleventhaspect of the present invention, since there are provided a plurality ofmagnets for magnetic levitation, the size of each such magnet is reducedand hence it is possible to handle the magnet more easily.

According to the rotary cathode X-ray tube equipment in the twelfthaspect of the present invention, since the mounting position of eachmagnet for magnetic levitation is adjustable, the gap between the magnetand the object to be attracted can be adjusted in accordance with themounting position of the magnet, so by mitigating the demand onmachining accuracy for each magnetic levitation magnet it is madepossible to facilitate the manufacture.

According to the rotary cathode X-ray tube equipment in the thirteenthaspect of the present invention, since plural magnets for magneticlevitation are provided and these magnets are attached to inner platesmounted to the vacuum vessel, the gap between each magnetic levitationmagnet and the object to be attracted can be adjusted in accordance withthe mounting position of the magnet, so by mitigating the demand onmachining accuracy for the magnet it is made possible to facilitate themanufacture.

According to the rotary cathode X-ray tube equipment in the fourteenthaspect of the present invention, out of magnets for magnetic levitation,the size of one having an attractive force component positioned in adirection to pull up the rotary member against gravity is larger thanthat of one having an attractive force component positioned in adirection to pull down the rotary member, so the size of a magnet formagnetic levitation which is not required to generate a large attractiveforce is made smaller, whereby the entire efficiency can be improved.

According to the rotary cathode X-ray tube equipment in the fifteenthaspect of the present invention, out of the total number of magnets formagnetic levitation, the number of magnets having an attractive forcecomponent positioned in a direction to pull up the rotary member againstgravity is larger than that of magnets having an attractive forcecomponent positioned in a direction to pull down the rotary member islarger, so by omitting the magnetic levitation magnets located inpositions not requiring the generation of a large attractive force, itis made possible to improve the entire efficiency.

According to the rotary cathode X-ray tube equipment in the sixteenthaspect of the present invention, since the equipment is provided with aninclination angle detecting mechanism for detecting an inclination angleof the vacuum vessel and also provided with a levitation magnet controlsection for increasing and decreasing the attractive forces of magneticlevitation magnets in accordance with output signals of the inclinationangle detecting mechanism, it is possible to reduce variations ofelectric current in the magnetic levitation magnets which occur uponinclination of the vacuum vessel relative to the subjects and hence itis possible to make a stable centroid position control.

According to the rotary cathode X-ray tube equipment in the seventeenthaspect of the present invention, since a front end of a yoke portion isdisposed within the vacuum vessel, a coil portion which evolves gas canbe disposed outside the vacuum vessel, whereby the degree of vacuum ofthe same vessel is improved.

According to the rotary cathode X-ray tube equipment in the eighteenthaspect of the present invention, since a non-contact type displacementmeter measures a displacement of an inclined surface of the object to beattracted, it is possible to let the non-contact displacement meterfunction to detect both a levitation state of the rotary member and aposition of the rotary member in the rotational axis direction, wherebythe number of such displacement meters used can be decreased, thuspermitting the reduction of size and cost.

According to the rotary cathode tube equipment in the nineteenth aspectof the present invention, since the non-contact displacement meters areattached to inner plates mounted to the vacuum vessel, it is easy tomake a fine adjustment of the mounting position of each non-contactdisplacement meter.

According to the rotary cathode X-ray tube equipment in the twentiethaspect of the present invention, since the equipment is provided with atleast one touch-down bearing whose central axis is separate from therotational axis of the rotary member, it is not necessary to use alarge-sized bearing and hence possible to attain the reduction of size,weight and cost.

According to the rotary cathode X-ray tube equipment in the twenty-firstaspect of the present invention, since the mounting position of thetouch-down bearing is adjustable, it is easy to make a fine adjustmentof the mounting position of the touch-down bearing.

According to the rotary cathode X-ray tube equipment in thetwenty-second aspect of the present invention, since the touch-downbearing is attached to an inner plate mounted to the vacuum vessel, itis easy to make a fine adjustment of the same bearing.

According to the rotary cathode X-ray tube equipment in the twenty-thirdaspect of the present invention, since within a movable range of atilting mechanism a centroid position of a portion tilted by the tiltingmechanism never assumes a position vertically below the rotational axisof the tilting mechanism and the centroid position is not coincidentwith the rotational axis of the tilting mechanism, it is possible toprevent the vacuum vessel, etc. from being oscillated about therotational axis by a reaction of the attractive force of each magneticlevitation magnet.

According to the rotary cathode X-ray tube equipment in thetwenty-fourth aspect of the present invention, since the equipment isprovided with a torque applying device for applying torque which isalways unidirectional to a rotative shaft of the tilting mechanism, thevacuum vessel, etc. can be prevented from being oscillated about therotational axis by a reaction of the attractive force of each magneticlevitation magnet.

According to the rotary cathode X-ray tube equipment in the twenty-fifthaspect of the present invention, the equipment is provided with arotational angle detecting means for detecting a rotational angle of therotary member, a non-contact displacement meter for detecting a positionof the rotary member, a memory section for storing a deformationquantity for each rotational angle of the rotary member, and adeformation correcting circuit for correcting a detected signal for eachrotational angle of the rotary member on the basis of an output signalfrom the rotational angle detecting means and the deformation quantity,so by allowing a certain deformation of the rotary member which is easyto deform due to a large size and difficult to improve in its machiningaccuracy, it is possible to attain a reduction in weight. Further, bymitigating the demand on machining accuracy, it becomes possible tofacilitate the manufacture.

According to the rotary cathode X-ray tube equipment in the twenty-sixthaspect of the present invention, since the drive means used is composedof a stator disposed on the side opposite to a subject insertion holewith respect to the vacuum vessel and a rotor disposed within the vacuumvessel and fixed to the rotary member, the movable range of the tiltingmechanism can be widened by decreasing the thickness of the equipment.

According to the rotary cathode X-ray tube equipment in thetwenty-seventh aspect of the present invention, the stator isconstituted by at least one rectilinear or arcuate stator, and thestator and the rotor constitute a linear induction motor, so by keepingthe mounting space for the stator to a minimum required, it is madepossible to attain the reduction of size and weight.

According to the rotary cathode X-ray tube equipment in the twenty-eightaspect of the present invention, since the yoke facing portion of theouter ring is thinner than the yoke non-facing portion thereof, it ispossible to obtain a large driving force of the motor.

According to the rotary cathode X-ray tube equipment in the twenty-ninthaspect of the present invention, the equipment is of a structure inwhich the object to be attracted reinforces the rotary members so byomitting the use of a special component for reinforcement it is possibleto attain a structural simplification and the reduction of weight.

According to the rotary cathode X-ray tube equipment in the thirtiethaspect of the present invention, the equipment is provided with anencoder for detecting a rotational angle of the rotary member, and thisencoder is composed of a light emitter and a photosensor which aredisposed on both sides of the rotary member, as well as a plurality ofdetection holes formed in the rotary member in positions where the lightfrom the light emitter passes, so by arranging the detection holes inspaced positions from the rotational axis of the rotary member, it ispossible to improve the detection accuracy. In addition, a highreliability is attained because of a non-contact structure.

According to the rotary cathode X-ray tube equipment in the thirty-firstaspect of the present invention, since the light emitter and thephotosensor are attached to inner plates mounted to the vacuum vessel,it is possible to facilitate a fine adjustment of the mounting positionsof the light emitter and the photosensor.

According to the rotary cathode X-ray tube equipment in thethirty-second aspect of the present invention, the equipment is providedwith a multiplying circuit, the multiplying circuit comprising a phasecomparator to which is inputted an output signal from an encoder, a VFconverter for converting an output signal of the phase comparator into apulse having a frequency proportional to the voltage thereof, and afrequency divider circuit which counts pulses provided from the VFconverter and outputs one pulse to the phase comparator at everycounting of a preset number, the phase comparator comparing the phase ofthe output signal from the encoder with that of the output signal fromthe frequency divider circuit. Therefore, by suppressing the number ofpulses of the output signal from the encoder, it becomes easy to machinethe detection holes in the rotary member and it is possible to use aphotosensor which is low in response frequency.

While preferred embodiments of the invention have been described usingspecific terms, such description is for illustrative purposes only, andit is to be understood that changes and variations may be made withoutdeparting from the spirit or scope of the following claims.

What is claimed is:
 1. A rotary cathode X-ray tube equipmentcomprising:a ring-shaped hollow vacuum vessel; a ring-shaped anodetarget fixed within said vacuum vessel; a ring-shaped rotary memberrotatably disposed in an opposed relation to said anode target withinsaid vacuum vessel; at least one cathode portion attached to said rotarymember on the side opposed to said anode target; an X-ray radiationwindow for passing X-rays generated at the anode target through thewindow, said X-ray radiation window being mounted to an inner ring ofsaid vacuum vessel; a rotary driving mechanism for rotationally drivingsaid rotary member, said rotary driving mechanism comprising a rotor; amagnetic levitation mechanism having a magnet for magnetic levitationwhich is fixed to said vacuum vessel; and an object to be attractedwhich is fixed to said rotary member wherein said object to be attractedis fixed in position between said rotary member and said rotor of saidrotary driving mechanism and integral with a portion of said rotor forreinforcing said rotary member.
 2. A rotary cathode X-ray tube equipmentaccording to claim 1, wherein said object to be attracted includes aninclined surface facing said magnet.
 3. A rotary cathode X-ray tubeequipment according to claim 2, wherein a non-contact type displacementmeter for detecting a position of said rotary member measures adisplacement of an inclined face of said object to be attracted fordetecting the displacements of each of rotary axis direction and radiusdirection of said rotary member by one displacement meter.
 4. A rotarycathode X-ray tube equipment according to claim 2, further comprising atleast one touch-down bearing for supporting said inclined surface ofsaid object to be attracted.
 5. A rotary cathode X-ray tube equipmentaccording to claim 1, wherein, said magnet for magnetic levitationcomprises a yoke portion and only said yoke portion is arranged in saidvacuum vessel.
 6. A rotary cathode X-ray tube equipment according toclaim 1, wherein a plurality of upper and lower magnets for magneticlevitation are provided so that the number of upper attractable magnetsis larger than lower attractable magnets.
 7. A rotary cathode X-ray tubeequipment according to claim 1, wherein a plurality of upper and lowermagnets for magnetic levitation are provided so that the upperattractable magnets are larger in size than the lower attractablemagnets.